Each airframe series has unique systems comprised of sensors, sensor data transmissson and / or filtering processes, flight system control computers, hydraulic actuators, and the software / electronic / mechanical glue that makes all those things sing together. Even if these are highly similar across related airframes, individual designs can have their own idiosyncratic problems.
The documented reports of tail-wiggling oscillations and eccentric responses to in-flight control actions suggest a real design problem might exist in the 600 rudder controls.
I would suggest that it is incumbent on Airbus to prove that they have designed to prevent such oscillations and tested to verify the correctness of the designs under all plausible flight conditions and maintenance scenarios. Can Airbus prove this? Almost certainly -- if it is true.